Parallel tube gaseous jet apparatus with multisize tube bores



E. c. BROWN 3,398,467

PARALLEL TUBE GASEOUS JET APPARATUS WITH MULTISIZE TUBE BORES Aug. 27,1968 Filed June 14, 1967 1 1 1 1 1 1 1 I I I 1 1 1 1 1 1 1 1 1 1 1 1 m 4l 4A 1 7 ll 1 1 6 1 1 Q A V 7 4 1 6 r |L 1 J .11 L G T I W A m A k n 15gW \IIH P\\\\A\\\\\\\\\ I 2 6 f 1 1 I 1 1 M 1 l yl l/l 1 l I I 1 1 1 1 11 1 1 1 1 1 1 United States Patent PARALLEL TUBE GASEOUS JET APPARATUSWITH MULTISIZE TUBE BORES Ernest C. Brown, Danvers, Mass., assignor toWolverine Corporation, Cambridge, Mass., a corporation of MassachusettsFiled June 14, 1967, Ser. No. 646,011

5 Claims. (Cl. 34-233) ABSTRACT OF THE DISCLOSURE In tube jet dryershaving a pattern of parallel tubes extending downwardly from a plenumfor directing high velocity gaseous jets onto a layer of particulatematerial being advanced transversely beneath the tube orifices, andwhere the tubes are given substantial length in order to provide exhaustpassageways of'large enough cross-sectional 'area to reduce the velocityof the exhausting gases sufficiently to prevent detrimental removal ofparticulate material to the exhaust system from the layer being treated,horsepower requirements for maintaining jet orifice exit velocities ator near the maximum as determined only by the requirement of causing nodetrimental particle removal to the exhaust system, are substantiallyreduced by giving the tubes enlarged cross-sectional bore areas in theirmajor upper section while retaining cylindrical bores of smallercross-sectional area extending for a distance of approximately fourtimes their diameter upwardly from the orifice ends so as not to changethe flow characteristics of the jets beyond the orifices from thoseproduced by tubes having the same orifice bore diameters but havingbores of uniform diameter throughout their lengths.

This invention relates to gaseous jet dryers of the type described inUnited States Patent No. 3,060,590 and more particularly to structuralimprovements which permit economic increase in drying capacity for agiven pattern and total cross-sectional area of jet orifices by reasonof increased jet orifice exit velocity and hence increased total volumeflow of drying medium in a given period of time.

In all gaseous jet treatment of particulate material in volvingdirecting high velocity gaseous jets downwardly onto a layer of separateparticles, as in the aforesaid patent, it is necessary, in withdrawingthe gaseous medium, that its velocity be rapidly reduced in order toprevent particles which have been fluidized by the jets from remainingentrained in the exhausting gaseous streams for such distances as to beseparated from the advancing layer of material being treated.

Such rapid decrease in velocity of the exhausting gases has beenaccomplished by delivering the gases through hollow tubes which aresuspended downwardly and parallelly from a common plenum and terminateat a proper distance above the layer of material to be treated whichadvances normal to the axes of the tubes. By this expedient, sufficientspace may be left between the parallel tubes to provide exhaust passageshaving the necessary minimum cross-sectional area so that as the gaswhich has issued downwardly out of the tube orifices and contacted theparticles being treated reverses its direction flow and ascends upwardlybetween the tubes it rapidly loses velocity because of the pressure dropprovided by the large cross-sectional areas between the tubes. Particlesfluidized by the jets thus fall back towards the layer rather than beingcarried into the exhaust system with the exhausting gaseous streams.

Particle treatment machines so designed have proved so efi'icient thatthere has been a substantial demand for increasing their capacitywithout increasing their length.

3,398,467 Patented Aug. 27, 1968 Any such increase in capacity requiresmovement of a greater quantity of gas in a given period of timenecessitating, for a given orifice pattern (number, arrangement andtotal cross-sectional area of orifices), increasing the exit velocity ofthe jets at each orifice. As the velocity is increased, however, for agiven crosssectional area of exhaust passageways, there is increasingdanger of entrained removal of the particles into the exhaust systemputting a practical upper limit in a given design on the orifice exitvelocity, governed by maintaining the exhaust velocity low enough toprevent removal of particles from the treating zone in the exhauststreams.

Accordingly, in order to permit higher orifice velocities, the exhaustpassages have been made of greater and greater cross-sectional area byextending the length of the tubes to add height to the cross-sectionalpassageways, thus accommodating greater orifice exit velocity withoutdetrimental entrainment of particles into the exhaust system ducts.

Such tube lengthenings have been routinely accompanied by provision forincreased blower horsepower to provide the increased plenum pressurenecessary to secure the increased orifice exit velocity. This hasinvolved additional initial expense for larger motors for driving theblowers and increased operating expense caused by the greater powerconsumption.

These additional expenses were,'however, readily accepted as a necessaryconcomitant of attaining the increased capacities.

The present invention is -founded upon the heretofore unappreciated factthat much of the increased horsepower so provided has been due, not tothe demand for increased orifice velocity, but to the tube lengthening.The longer the tube of a given bore diameter, the greater the pressurerequired in the plenum to maintain a given velocity at the orifice.

It was then realized that, so long as the tube bores retained theirdesired orifice cross-sectional area upwardly for a sufiicient distanceto insure that the flow characteristics of the gases emanating from theorifice would remain unaffected, it was entirely unnecessary to continuethe same cross-sectional bore area for the remainder of the length ofthe tube all the way up to the plenum. In addition it was found that asmall enlargement of the bores in the upper portions of the tubes (andhence of the OD. of the tubes in the case of cylindrical tubes) did notso seriously detract from the total cross-sectional exhaust passage areaas to cause entrainment of particles even at the substantially greaterorifice exit velocities.

Accordingly, in apparatus of this invention, tubes are utilized whichare characterized by the fact that they have bottom sections havingwalls defining cylindrical bores of equal diameters and of uniformlengths approximating four times their bore diameters. That geometryfurnishes the same flow characteristics beyond the orifice that occurswith a bore of uniform diameter and infinite length at the same exitvelocity. The bottom sections then are surmounted with walls formingbores slightly tapering outwardly and upwardly and merging into bores,of greater cross-sectional area than the orifice cross-sectional area,extending the remainder of the total length of the tubes. For example,where a tube is 21 inches in length, it is provided with a circularbottom orifice formed by the bore of a inch O.D. ZO-gauge tube extendingupwardly for 3 inches from the end of the tube. The remainder of thetube is made of l-inch O.D. ZO-gauge tubing, connected by a sectionhaving a conical bore to the bottom 3-inch section. The consequenceswill be further described after reference is made to the accompanyingdrawing showing a typical embodiment of the invention and wherein FIG. 1is a fragmentary transverse cross-sectional view p 1 .-"'3,398,46 7, g v

of a jet dryer. apparatus,-.broken away to indicate extent. similar tothe dryer shown in FIG. 3 of U.S. Patent No. 3,060,590; and

FIG. 2 is an enlarged detail of one of the jet tubes.

The apparatus includes a casing 60 within which are suspended walls 61forming a plenum 62 beneath and along the sidesof which are exhaustpassageways 64 and 66leading to a fan (not shown) which may return theair to plenum 62 where it is heated by a heater 54 or by other means.

The tubes 70 extend downwardly from the plenum towards a conveyor 72which supports particles to be treated in layer A. Suitable seals 74embrace the lateral edges of the conveyor to restrict intake of air.

Cylindrical tubes 70 have a major upper section 76 of larger boreconnected by a conical section 78 to a lower bore 80 of smallercross-sectional area, all being identical and-formed most easily byswaging the bottom section to the configuration shown.

In order to illustrate the eifectiveness of structures embodying theinvention, one may take, for example, a construction utilizing a 22 inchlong tube. If the bore of this tube is of a diameter corresponding tothe ID. of a inch O.D. 20-gauge tube throughout its total length, itwould be necessary, in order to provide an orifice velocity of 12,000cubic feet per minute to have a pressure at the orifice of 8.97 incheswater gauge. To secure this orifice pressure, it would be necessary tohave a plenum pressure of 11.38 inches water gauge. However, byenlarging the upper section of the tube so it corresponds in borediameter to the bore diameter of a 1-inch ZO-gauge tube, the sameorifice pressure of 8.97 inches water gauge can be obtained utilizingonly 9.42 inches water gauge pressure in the plenum. As thus can beseen, saving in horsepower resulting from the lower operating level ofplenum pressure can be substantial. Obviously the saving in horsepowercannot be accomplished by enlarging the cross-sectional diameter of thebore throughout its entire length because such enlarged area at theorifice will act to reduce the velocity in accordance with the equationNor can the saving be effected by tapering the tubes to a minimum areaorifice without loss of the desired quasi laminar flow pattern.

The objects of the invention are thus obtained by retaining so much ofthe small tube structure at the bottom to retain the desired flowcharacteristics beyond the orifices and then modifying the upper tubestructure, which does not anyway aifect the flow characteristics beyondthe orifice, for the purpose of reducing the pressure required in theplenum to maintain the desired pressure and velocity at the orifice. Ingeneral, the small bore section should be in length approximately fourtimes its bore diameter and no more.

a i It is to be understood that FIG. 1 shows only one traverse row oftubes, but the apparatus will have a multiplicity of rows preferably toform a staggered diamond pattern as shown in FIG. 2 of US. Patent No.3,060,595 with the orifice cross-sectional areas constituting usuallyonly about 4% of the total area of the target area in the treating zone;I

What is claimed is:

1. Apparatus for treating particulate material with high velocitygaseous jets having means for supporting and advancing a layer ofparticulatematerial to be treated and means for directing parallelspaced jets of gas downwardly onto said layer as-itadvances, including aplenum overlying said layer and a pattern of spaced parallel hollowtubes extending from the bottom wall of said plenum downwardly towardssaid layer supporting means with the spaces between the tubes formingpassageways for exhausting gases emanating from said tubes upwardly andaway from said supporting means, said apparatus being characterized bythe fact that the bottom sections of said tubes have walls definingcylindrical bores of equal diameters and of uniform lengthsapproximating four times their bore diameters, said bottom tube,sections being surmounted by upper tube walls defining bores slightlytapering upwardly and outwardly from said bottom sections and merginginto bores of larger crosssectional area than the bores of said bottomsections, said larger bores extending upwardly throughout the remainingportions of said tubes to the points of their separate communicationwith said plenum.

2. Apparatus as claimed in claim 1, wherein the bores of largercross-sectional area in the upper section of said tubes extend the majorlength of said tubes.

3. Apparatus as claimed in claim 1, wherein the ratio of the totallength of the tubes to the length of said bottom tubesections is about7:1.

4. Apparatus as claimed in claim 1, wherein the walls of the bottomsections of said tubes are swaged in from the upper tube walls to formthe smaller bores at the bottoms of said tubes.

5. Apparatus as claimed in claim 1, wherein the bore of each tubeconsists of an upper cylindrical bore of larger diameter and alowercylindrical bore of smaller diameter joined by a connecting conicalbore.

References Cited UNITED STATES PATENTS 2,724,907 11/ 1955 Walter 34-160XR 3,060,590 10/1962 Brown 34233 XR 3,060,595 10/1962 Dapses 343,140,157 7/1964 Fleissner et al. 34-160 3,176,412 4/1965 Gardner 34160XR 3,199,224 8/1965 Brown 34160 XR 3,359,648 12/1967 Overly et al34--162 XR FREDERICK MATTESON, IR., Primary Examiner. A. D. HERRMANN,Assistant Examiner.

